/*****************************************************************************
*
* read_random_big.c 2012.07.04 Smythies
*     This program needs to also work when compiled and executed on 32 bit
*     computers. Try to make 64 or 32 bit independent.
*     Troubles with fseek on 32 bit, try lseek.
*
* read_random_big.c 2012.07.03 Smythies
*     Change the method of printing information away from per number of seeks
*     and to some delta time. The seek time is highly inconsistant.
*
* read_random_big.c 2012.07.02 Smythies
*     Read random locations of blocks of data in a big file.
*     The file was likely created by trandbig.c
*     The purpose is to create a situation of large amount of time spent
*     doing seeks, or a lrage percentgae of time in an IO wait state.
*     This seems to be pretty slow at doing seeks, but the point is to create
*     IO wait time, so O.K.
*                                                                     Smythies
*****************************************************************************/

#define _FILE_OFFSET_BITS 64

#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/times.h>
#include <time.h>
#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
//#include <conio.h>

#define GIGS 8
#define WRITE_SIZE 1048576
#define PRINT_INTERVAL 60.0
#define THRESHOLD 0.1

char buffer[WRITE_SIZE];

main(){
   clock_t start, end, last;
   struct tms t_start, t_end;
   char temp;
   int the_byte;
   long j, tps, multiplier, old_seeks;
   long long i, old_i, total_bytes, the_return_code;
   double elapsed, next, delta, longest;
   unsigned inf;

   if((inf = open("big",O_RDONLY)) == -1){
      printf("Unable to open input file\n");
      exit(-1);
   } /* endif */

   srand(31);
   total_bytes = (long long) GIGS * (long long) WRITE_SIZE * (long long) 1024;
   multiplier = total_bytes / RAND_MAX;
   j = 0;
   old_seeks = 0;

// printf("read_random_big: LONG_MAX: %ld   RAND_MAX: %d\n", 7l, RAND_MAX);
   printf("read_random_big: total bytes in file \"big\" (a compile time number): %lld  multiplier: %ld\n", total_bytes, multiplier);

   tps = sysconf(_SC_CLK_TCK);
   start = times(&t_start); /* */
   end = start;
   next = PRINT_INTERVAL;
   old_i = 0;
   longest = 0.0;
   while(1){   /* forever */
      i = (long long) rand();
      i = i * multiplier;
      the_return_code = lseek(inf, i, SEEK_SET);
//    printf("read_random_big: %ld  %d\n", i, the_return_code);
      if(the_return_code == -1){
         printf("some file seek error\n");
         exit(1);
      } /* endif */
      if(the_return_code != i){
         printf("seek offset not as asked for: %lld  %lld\n", the_return_code, i);
         exit(1);
      } /* endif */
      the_byte = read(inf, buffer, 1); /* fetch an actual byte from the location  */
      j++;
      last = end;
      end = times(&t_end); /* */
      delta = (double)(end - last) / (double)(tps); /* */
      elapsed = (double)(end - start) / (double)(tps); /* */
      if(delta > longest){
         longest = delta;
         printf("read_random_big: New longest seek time: %5.2lf seconds. Seek number: %7ld  (%lld %lld)\n", delta, j, i, old_i);
      } /* endif */
      if(delta >= THRESHOLD){
         printf("read_random_big: Excessive seek time: %5.2lf seconds. Seek number: %7ld  (%lld %lld)\n", delta, j, i, old_i);
      } /* endif */
     if(elapsed >= next){
         printf("read_random_big:%7ld seeks: (%5.0lf /s (last)) elapsed time: %7.1lf seconds ", j, (double) (j - old_seeks) / (PRINT_INTERVAL + elapsed - next), elapsed);
         printf("user cpu:%7.2f s. ", ((float)(t_end.tms_utime) / (float) (tps)));
         printf("sys cpu:%7.2f s. ", ((float)(t_end.tms_stime) / (float) (tps)));
         printf("longest seek: %6.3f s. ", longest);
         printf("\n");
         next = next + PRINT_INTERVAL;  /* prevents accumulation of errors */
         old_seeks = j;
      } /* endif */
      old_i = i;
   } /* endwhile */
   close(inf);  /* it never actually gets here */
   return(0);
} /* endprogram */